Java — Overview

What is Java?

Java is a class-based, object-oriented programming language designed to be "write once, run anywhere" (WORA). Java code compiles to bytecode that runs on the Java Virtual Machine (JVM), making it platform-independent.

Released in 1995 by Sun Microsystems (now Oracle), Java remains one of the most popular languages in the world — used for enterprise backend systems, Android apps, big data (Hadoop, Spark), and financial systems.

Why Learn Java?

•Huge job market — most banking, insurance, and enterprise companies use Java

•Android development — primary language for Android (alongside Kotlin)

•Enterprise frameworks — Spring Boot, Jakarta EE power millions of applications

•Strong typing — catches errors at compile time

•Excellent tooling — IntelliJ IDEA, Eclipse, Maven, Gradle

Java Versions

Version	Year	Key Features

|---|---|---|

Java 8 LTS	2014	Lambda expressions, Stream API, Optional
Java 11 LTS	2018	HTTP client, local variable type inference
Java 17 LTS	2021	Records, sealed classes, pattern matching
Java 21 LTS	2023	Virtual threads, sequenced collections

LTS versions (8, 11, 17, 21) are supported for years — use Java 17 or 21 for new projects.

Install Java

bash

# Ubuntu/Debian
sudo apt update
sudo apt install openjdk-21-jdk
java -version

# macOS (Homebrew)
brew install openjdk@21
java -version

# Windows: download from adoptium.net (Temurin OpenJDK)

# Verify
javac -version   # Java compiler
java -version    # Java runtime

Hello World

java

// HelloWorld.java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");

        // Variables
        String name = "SynfraCore";
        int year = 2025;
        double price = 99.99;

        // String formatting
        System.out.printf("Learning Java at %s in %d%n", name, year);
        System.out.println("Price: ₹" + price);
    }
}

bash

# Compile and run
javac HelloWorld.java    # Creates HelloWorld.class
java HelloWorld          # Runs the bytecode
# Output: Hello, World!

Java in the DevOps World

Java is everywhere in the infrastructure you manage:

•Jenkins is written in Java — understanding Java helps customize it

•Elasticsearch is Java — JVM tuning is critical for performance

•Kafka is Java/Scala — understanding the JVM helps with heap tuning

•Spring Boot microservices — most enterprise microservices are Spring Boot

Course Sections

•Fundamentals — variables, control flow, methods, OOP basics

•Intermediate — collections, generics, exception handling, file I/O

•Advanced — multithreading, Spring Boot, JVM tuning, design patterns

•Labs — coding exercises with JUnit testing

•Interview — 50 most asked Java interview questions

Java Programming — Overview